Dynamic magnetic information storage or retrieval – Head – Read only detector using light for reading magnetically...
Patent
1991-05-02
1993-07-13
Heinz, A. J.
Dynamic magnetic information storage or retrieval
Head
Read only detector using light for reading magnetically...
G11B 5127
Patent
active
052279383
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high resolution magneto-optic read head.
2. Discussion of the Background
The magneto-optic reading of magnetic tapes or disks using the Faraday effect in a ferrimagnetic garnet placed in contact or close to the magnetic medium is known for example from publications by T. NOMURA (NHK Company). Such a reading mode gives good performance with regard to the minimum detectable signal level (when its amplitude is close to the average amplitude of the noise), in particular for recording on narrow tracks. On the other hand, this reading mode has a rather low resolution, limited both by the resolution of the optical system and by the spatial band (natural dimensions of the domains) of the garnet. It is thus difficult to read signals having wavelengths of less than one micrometer, whereas present-day magnetic tapes allow the recording of signals having wavelengths of 0.5 micrometer or less.
T. NOMURA has described a solution associating with the garnet used as a magneto-optic transducer a magnetic structure providing coupling with the magnetic tape. This structure is a pole piece having microscopic dimensions (thickness 0.6 .mu.m, track width 15 .mu.m, height 25 .mu.m) applied and stuck to the garnet.
It would be possible to consider the use of magneto-optic transducers for the reading of high density multi-track magnetic recordings, but the major problem which arises then is cross talk between tracks. T. NOMURA's present device would not allow such a multi-track device to be produced because of the high track-to-track permeance exhibited by the pole piece. It would be necessary to divide up this pole piece which would present very large production problems.
SUMMARY OF THE INVENTION
The subject of the present invention is a magneto-optical read head which can advantageously be a multi-track read head, which is easy to produce, has the lowest possible cost price and which has both a high resolution and the lowest possible cross talk if it is a multi-track head.
The magneto-optic read head according to the invention comprises at least one micro-head formed on a substrate, this micro-head comprising a magneto-optic transducer and at least two pole pieces made of magnetic material separated by a narrow air-gap. Preferably, the transducer and the pole pieces are formed using the thin-layer technique. Advantageously, it is possible to modify locally the magnetic properties of the pole pieces, for example by modifying their geometry and/or their composition. It is possible, also advantageously, to apply to the magneto-optic transducer a variable magnetic or electromagnetic field.
According to an advantageous variant of the invention, the material of the magneto-optic transducer exhibits an oblique anisotropy and is monodomain over at least one of the pole pieces.
The present invention will be better understood on reading the detailed description of several embodiments, taken by way of non-limitative examples and illustrated by the appended drawing in which:
FIG. 1 is a simplified perspective view of a magneto-optic read head of the prior art,
FIGS. 2 and 2A are respectively a simplified perspective view of a magneto-optic read head according to the invention and a simplified cross-sectional view of a variant of the head according to the invention,
FIG. 3 is a simplified partial view of an embodiment of a magneto-optic read head according to the invention,
FIG. 4 is a diagrammatic cross-sectional view of a read head according to the invention showing field lines which it generates,
FIG. 5 is a set of diagrammatic cross-sectional views of a read head according to the invention, showing the displacement of the boundaries of the domains of the magneto-optic transducer under the effect of the field generated by a magnetic dipole,
FIG. 6 is a simplified diagram of an embodiment of a magneto-optic read system comprising a read head according to the invention,
FIGS. 7a, 7b and 7c are a set of diagrammatic cross-sectional views showing vari
REFERENCES:
patent: 4618901 (1986-10-01), Hatakeyama et al.
patent: 4677513 (1987-06-01), Naito et al.
patent: 4707755 (1987-11-01), Ohta
Patent Abstracts of Japan, vol. 12, No. 34 (P-662) (2881), Feb. 2, 1988 & JP, A, 62185267 (Hitachi) Aug. 13, 1987.
Colineau Joseph
Neubert Sophie
"Thomson-CSF"
Heinz A. J.
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